Cathode ray apparatus



June 11, 1935. A V. VBEDFORD 2,004,099

CATHODE RAY APPARATUS Filed o ct, 15, 1952 H I [WEA/Toe: @am @4gb Alda www@ Patented .inne 1935 My invention relates to imp vision systems.

anotan EN'I` OFFECI- CATHODE RAY APPARATUS Alda V. Bedford, Collingswood, N. 5 assignor to Radio Corporation of America, New York, N. Y., a corporation of' Delaware Application October 15, 1932, Serial No. 637,879

9 Claims;

rovements in tele- In television systems embodying a cathode ray tube at the transmitting station, and in which the 5 tube comprises a photo-sensitive mosaic screen on which an image of the object is projected, it has been found to be advantageous to scan, by the cathode ray, the same side of the screen on which the image is projected. When this is done, the axis of the optical system for projecting the image is made perpendicular to the screen, but

the axis of the s45-called gun for developing and directing the ray of electrons is, of necessity, disposed at an acute angle to the screen. On Iaccount of this arrangement, the outline of the area scanned by the ray has a keystone shape' rather than the desired rectangular shape. The distortion of the scanned pattern is manifested by a substantial and corresponding distortion of the reproduced image at the receiving station,

the reproduced image being also the shape of a keystone, with the vertical lines inclined to each other.

With the foregoing in mind, it is one of the objects of my invention tov provide an improved television system oi. the character referred to wherein the keystone distortion is corrected.

Other objects and advantages will hereinafter appeal'.

In accordance with my invention, the cathode ray is deiiected horizontally by electromagnetic coils provided with pole pieces shaped to' cause *the lines of ux to spread voutwardlyior diverge from one pole piece to the other in planes perpendicular to the axis of the electron gun.

In this scan the surface thereof over a substantially rectangular area.

My invention resides in the improved apparatus of the character hereinafter described and claimed.

wherein Figure 1 is a perspective view, partly diagrammatic, of television transmitting apparatus embodying my invention;

Figs. 2 and 3 are slmplied, sectional views, the

sections being taken, respectively, on the lines 2--2 and 3 3 in Fig. 1; and

Figs. 4 and 5 are simplified, fragmentary view showing several modifications.

With reference to Fig. i, the reference numeral Iii designates a cathode ray tube provided with some suitable form of mosaic photosensitive screen structure l2 upon which an image of the object is projected., The screen strucn ture 'i2 comprises, generally, a supporting plate provided on the front surface thereof withia great number of minute metallic elements (not shown) insulated from each other and from the plate, and each provided with a coating of photosensitive material. A

An image of the object, shown as being in the form of a moving picture film it, is projected upon the photosensitive surface by a suitable optical system It, the axis i8 of which is perpendicular to the'screen structure i2.

An electron gun 20, of any suitable construction, operates to develop a ray 22 of electrons, and to direct the ray at the photosensitive surface of the screen l2, the axis 24 of the tube being inclined at an acute angle of about i to the'plane' of the screen i2.

For` the purpose of causing the ray 22 to sean the photosensitive surface of the screen I2, sawtooth current Waves at diiferent frequencies are caused to flow through the coils 26, 23, 313, and 32. The coils 26 and 3U operate to deflect the ray vertically, while the coils 28 .and 32 operate to deect the ray horizontally.

As shown, the vertical and horizontal deflecting coils are placed on separate yokes 3d and 36, the yoke carryingthe vertical deflecting coils 26 and 38 being disposed next to the electron gun 28 so that the ray 22 passes first through the vertical deecting field before it passes through the horizontal deiiecting field. The yokes 34 and 36 are spaced a suflicient distance from. each other to insure against detrimental fiux inter-leakage.

As more clearly shownin Fig. 2, the pole pieces 38 and'd have different shapes, the pole piece 38 being larger and curved so that the lines of ux 42 converge downwardly. In this-way,

the flux density is made to inc'rease uniformoi' the screen i 2, it is caused to scan the same over a substantially rectangular area. Without this action, to correct for the keystone distortion, the ray would scan the screen I2 over a keystone area, as indicated in Fig. 1.

Other possible variations of the pole pieces I8 and 40 are shown in Figs. 4 and 5. In Fig. 4, the upper polepiece 38a is greater in cross sectional area than the lower pole piece section 40a, and has a concave face. In Fig.` 5, the upper pole piece 38h is` T-shaped, the upper face *thereof4 ybeing flat and greater in area than the complementary face of thev lower pole piece 4017.

In some cases, there might remain some slight distortion at the corners of the area over which the ray' 22 scans the screen l2. To correct for this, it is proposed to place permanent magnets 44 in suitable positions to shape themagnetic field in such manner as to eliminate the relatively slight remaining distortion.

It will be understood that various modiiication Within the conception of those skilled in the art are possible without departing from the spirit of my invention or the scope of the claims.

I claim as my invention: y

1. Cathoderay apparatus comprising screen structure and an electron gun for developing a ray of electrons and directing the same 'at said structure, the axis of said gun being disposed at an acute angle to said structure, and meansg'for deecting said ray to cause the same to scan a keystone area over a plane perpendicular to said axis whereby the ray is caused to scan said of .said axis and shaped and arranged to cause the magnetic lines of force to diverge substanltially uniformly from one edge of the area traversed by the ray to the opposite edge oi such area.

2. Cathode ray apparatus comprising screen structure and an. electron gun for developing a ray of electrons and directing the same at said structure, the axis of said gun being disposed at an acute angle to said structure, and means for deflecting said ray to cause the same to scan a keystone area over a plane perpendicular to said axis whereby the ray is caused to scan said structure over a substantially rectangular area, said ray-deflecting means including magnetic pole pieces disposed respectively cn opposite sides of said axis, the dimension oi' the tace of one of said pole pieces measured transversely of said axis being substantially greater than such dimension of the face of the opposite pole piece.

3, Cathode ray apparatus comprising screen structure and an electron gun for developing a ray of electrons and directing the same at said structure, the axis of said gun being disposed at acute angle to said structure, and means ior deiiectingsaid ray to cause the saine to scan a keystone area over a plane perpendicular to said axis whereby the -ray is caused to scan said structure over a substantially rectangular area; said ray at a relatively low frequency, and a second magnetic core disposed about said axis between said screen structure and said mst-named core and spaced from the latter, said second core being provided with pole pieces, and coils carried by said second-named pole pieces for deilecting said ray at a relatively high frequency.

4. Cathode rayl apparatus comprising scre'en structure and an electron gun for developing a ray of electrons and directing the same at said structure, the axis oi'said gun being disposed at an acute angle to said structure, and means for deilecting said ray'iiorizontally and vertically to cause the same toscan a keystone area over a plane perpendicular to said axis whereby the ray is caused to scan said structure over a substantially rectangular area; said ray-deecting means including a magnetic core disposed about said axis and adjacent said ray-developing means and provided with pole pieces, coils carried by said pole pieces for deecting said ray vertically, and a second magnetic core disposed about said axis between said screen structure and said ilrstnamed core and spaced from the latter, said second core being provided with pole pieces, and coils carried by said second-named pole pieces for defiecting said ray horizontally.

5. Cathode ray apparatus comprising screen structure and an electron gun for developing a ray of electrons and directing the same at said structure, the axis of said gun being disposed at an'acute angle to said structure, and means for deiiecting said ray to cause the same to scan a keystone area over a plane perpendicular to said axis whereby the ray is caused to scan said structure over a substantially rectangular area, said ray-deilecting means including a plurality of magnetizable and complementary poles having dissimilar opposed ends and arranged to cause the magnetic lines of force to .diverge substantially uniformly from one edge of the area traversed by the ray to the opposite edge of such area.

6. 'I'he invention set forth in claim 5 characterized in that one of the pole-faces has a greater area than the other pole-face.

7. The invention set forth in claim 5 characterized in that one of the pole-faces is curved from one edge/ thereof to the opposite edge on' substantially an arc of a circle.

8. The invention set forth in claim 5 charactirized in that one of the poles is T-shaped and has its face curved from one edge thereof to the opposite edge onsubstantially an arc oi a circle. 9. The invention set forth in claim 5 charactirized in that one of the poles is T-shaped and 60 

